1. Field of the Invention
The present invention relates generally to a drive circuit device for a display device such as a liquid crystal display device, and more particularly, to a drive circuit device that can reduce power consumption and suppress occurrence of electromagnetic waves.
2. Description of the Related Art
The liquid crystal display device is now widely being used for the monitor screen of a computer, etc., because of its space-saving feature. In recent years, a larger type is further being called for, and development of structure to meet the requirement is increasingly being made.
Of the liquid crystal display devices, a liquid crystal display device of an active-matrix type has pixels in a matrix arrangement, using active elements, like TFTs (thin film transistors). This liquid crystal display device has pixel electrodes and a common electrode on a liquid crystal display panel or substrate, and a liquid crystal layer between them. Further, the liquid crystal display panel has source bus lines and gate bus lines, which cross each other, and TFTs provided at the crossing positions. And, by driving the gate bus lines to cause the TFTs of the pixels located in the row direction to a conductive state, and applying voltage corresponding to the half tone of the pixel to each source bus line, the voltage corresponding to the half tone of the pixel is applied between the pixel electrode and the common electrode. As the result of the application of voltage, the liquid crystal layer between the pixel electrode and the common electrode has a transmission factor corresponding to the applied voltage, thereby allowing a reproduction of an expected half tone to be possible.
In order to perform such display operations, a gate driver which sequentially drives the gate bus lines, and a source driver which drives the source bus lines simultaneously with the voltage corresponding to the displayed data, are connected to the liquid crystal display panel. The gate driver and the source driver will be embodied by an integrated circuit device, and each of the drivers drives a plurality of gate bus lines or a plurality of source bus lines, respectively. Therefore, in order to drive many gate bus lines and the source bus lines on the display circuit board, a plurality of the gate drivers and source drivers must be connected to the area around the liquid crystal display panel.
With the requirement for space saving, the downsizing of the liquid crystal display device seems to be the current trend, but, on the other hand, to meet the request for larger size of the monitor screen, a space for packing the gate driver and the source driver is becoming limited. With this limitation, signal lines for the data signal, clock signal or control signal to be supplied to the plurality of the source drivers and the gate drivers are formed on an LCD panel, on which TFT source bus lines and gate bus lines for the liquid crystal display panel are installed.
Unlike a printed circuit board, the signal lines to be formed on the liquid crystal display panel has relatively higher resistance and capacitance compared with a printed circuit board, and cannot be covered with a ground wiring layer. For this reason, when pulse signal with high frequency is applied to these signal lines, a lot of power is consumed to drive these signal lines, and a strong electromagnetic wave will be sent out along with the driving. Especially, along the upsizing of the screen, the number of the driver Ics will be increased, and further, the signal lines for propagating the data signal, clock signal, or control signal becomes longer, so that the power consumption and occurrence of electromagnetic wave is considerably increased.